Field of the Invention
The invention relates to a method of operating equipment for coating printing materials in a printing press. The invention also relates to equipment for coating printing materials in a printing press.
German Published, Non-prosecuted Patent Application DE 197 57 094 A1, corresponding to British Patent 2 232 394, discloses equipment for coating printing materials in a printing press, which has a metering system that, with the aid of a circulating-pipeline system, can be supplied with a liquid coating medium, for example varnish, in a container. The circulating-pipeline system includes a feed pump for feeding the coating medium to the metering system and two suction pumps, by which the coating medium is conducted back from the metering system into the container. In order to clean a feed line disposed downstream of the feed pump and leading to the metering system, the metering system itself and return lines leading from the metering system to the container, the lines must first be emptied. In order to empty the feed line, an additional, i.e., a third, suction pump is provided, which serves only for emptying the feed line, the suction side of the third suction pump being connected to the feed line via a bypass and the pressure side of the third suction pump being connected to the container via a fluid connection. Because of the many pumps, the costs and the space required for this equipment are correspondingly high. In a second alternative embodiment, the extraction of the feed line is performed only by the feed pump, which is of convertible construction for interchanging the suction and pressure region thereof, so that the feed line is connected as desired either to the pressure side or the suction side of the feed pump.
U.S. Pat. No. 2,545,445 discloses equipment having a metering system to which a circulating-line system is assigned which includes a feed pump and a return pump, which are mutually coupled and driven by a motor. In order to divide the fluid stream leading to the metering system via a feed line, a fluid connection disposed between the feed line and the suction region of the return pump is provided, which can be shut off by a valve device. A disadvantage of this equipment is that automatic or automated emptying of the feed line is not possible therewith.